 /*
  * $Header: /cvshome/build/org.osgi.framework/src/org/osgi/framework/BundleContext.java,v 1.22 2007/02/21 16:49:05 hargrave Exp $
  *
  * Copyright (c) OSGi Alliance (2000, 2007). All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  * http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package org.osgi.framework;

 import java.io.File ;
 import java.io.InputStream ;
 import java.util.Dictionary ;

 /**
  * A bundle's execution context within the Framework. The context is used to
  * grant access to other methods so that this bundle can interact with the
  * Framework.
  *
  * <p>
  * <code>BundleContext</code> methods allow a bundle to:
  * <ul>
  * <li>Subscribe to events published by the Framework.
  * <li>Register service objects with the Framework service registry.
  * <li>Retrieve <code>ServiceReferences</code> from the Framework service
  * registry.
  * <li>Get and release service objects for a referenced service.
  * <li>Install new bundles in the Framework.
  * <li>Get the list of bundles installed in the Framework.
  * <li>Get the {@link Bundle} object for a bundle.
  * <li>Create <code>File</code> objects for files in a persistent storage
  * area provided for the bundle by the Framework.
  * </ul>
  *
  * <p>
  * A <code>BundleContext</code> object will be created and provided to the
  * bundle associated with this context when it is started using the
  * {@link BundleActivator#start} method. The same <code>BundleContext</code>
  * object will be passed to the bundle associated with this context when it is
  * stopped using the {@link BundleActivator#stop} method. A
  * <code>BundleContext</code> object is generally for the private use of its
  * associated bundle and is not meant to be shared with other bundles in the
  * OSGi environment.
  *
  * <p>
  * The <code>Bundle</code> object associated with a <code>BundleContext</code>
  * object is called the <em>context bundle</em>.
  *
  * <p>
  * The <code>BundleContext</code> object is only valid during the execution of
  * its context bundle; that is, during the period from when the context bundle
  * is in the <code>STARTING</code>, <code>STOPPING</code>, and
  * <code>ACTIVE</code> bundle states. If the <code>BundleContext</code>
  * object is used subsequently, an <code>IllegalStateException</code> must be
  * thrown. The <code>BundleContext</code> object must never be reused after
  * its context bundle is stopped.
  *
  * <p>
  * The Framework is the only entity that can create <code>BundleContext</code>
  * objects and they are only valid within the Framework that created them.
  *
  * @ThreadSafe
  * @version $Revision: 1.22 $
  */

 public interface BundleContext {
     /**
      * Returns the value of the specified property. If the key is not found in
      * the Framework properties, the system properties are then searched. The
      * method returns <code>null</code> if the property is not found.
      *
      * <p>
      * The Framework defines the following standard property keys:
      * </p>
      * <ul>
      * <li>{@link Constants#FRAMEWORK_VERSION} - The OSGi Framework version.
      * </li>
      * <li>{@link Constants#FRAMEWORK_VENDOR} - The Framework implementation
      * vendor.</li>
      * <li>{@link Constants#FRAMEWORK_LANGUAGE} - The language being used. See
      * ISO 639 for possible values.</li>
      * <li>{@link Constants#FRAMEWORK_OS_NAME} - The host computer operating
      * system.</li>
      * <li>{@link Constants#FRAMEWORK_OS_VERSION} - The host computer
      * operating system version number.</li>
      * <li>{@link Constants#FRAMEWORK_PROCESSOR} - The host computer processor
      * name.</li>
      * </ul>
      * <p>
      * All bundles must have permission to read these properties.
      *
      * <p>
      * Note: The last four standard properties are used by the
      * {@link Constants#BUNDLE_NATIVECODE} <code>Manifest</code> header's
      * matching algorithm for selecting native language code.
      *
      * @param key The name of the requested property.
      * @return The value of the requested property, or <code>null</code> if
      * the property is undefined.
      * @throws java.lang.SecurityException If the caller does not have the
      * appropriate <code>PropertyPermission</code> to read the
      * property, and the Java Runtime Environment supports permissions.
      */
     public String getProperty(String key);

     /**
      * Returns the <code>Bundle</code> object associated with this
      * <code>BundleContext</code>. This bundle is called the context bundle.
      *
      * @return The <code>Bundle</code> object associated with this
      * <code>BundleContext</code>.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      */
     public Bundle getBundle();

     /**
      * Installs a bundle from the specified location string. A bundle is
      * obtained from <code>location</code> as interpreted by the Framework in
      * an implementation dependent manner.
      * <p>
      * Every installed bundle is uniquely identified by its location string,
      * typically in the form of a URL.
      *
      * <p>
      * The following steps are required to install a bundle:
      * <ol>
      * <li>If a bundle containing the same location string is already
      * installed, the <code>Bundle</code> object for that bundle is returned.
      *
      * <li>The bundle's content is read from the location string. If this
      * fails, a {@link BundleException} is thrown.
      *
      * <li>The bundle's <code>Bundle-NativeCode</code> dependencies are
      * resolved. If this fails, a <code>BundleException</code> is thrown.
      *
      * <li>The bundle's associated resources are allocated. The associated
      * resources minimally consist of a unique identifier and a persistent
      * storage area if the platform has file system support. If this step fails,
      * a <code>BundleException</code> is thrown.
      *
      * <li>If the bundle has declared an Bundle-RequiredExecutionEnvironment
      * header, then the listed execution environments must be verified against
      * the installed execution environments. If none of the listed execution
      * environments match an installed execution environment, a
      * <code>BundleException</code> must be thrown.
      *
      * <li>The bundle's state is set to <code>INSTALLED</code>.
      *
      * <li>A bundle event of type {@link BundleEvent#INSTALLED} is fired.
      *
      * <li>The <code>Bundle</code> object for the newly or previously
      * installed bundle is returned.
      * </ol>
      *
      * <b>Postconditions, no exceptions thrown </b>
      * <ul>
      * <li><code>getState()</code> in {<code>INSTALLED</code>,<code>RESOLVED</code>}.
      * <li>Bundle has a unique ID.
      * </ul>
      * <b>Postconditions, when an exception is thrown </b>
      * <ul>
      * <li>Bundle is not installed and no trace of the bundle exists.
      * </ul>
      *
      * @param location The location identifier of the bundle to install.
      * @return The <code>Bundle</code> object of the installed bundle.
      * @throws BundleException If the installation failed.
      * @throws java.lang.SecurityException If the caller does not have the
      * appropriate <code>AdminPermission[installed bundle,LIFECYCLE]</code>, and the
      * Java Runtime Environment supports permissions.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      */
     public Bundle installBundle(String location)
             throws BundleException;

     /**
      * Installs a bundle from the specified <code>InputStream</code> object.
      *
      * <p>
      * This method performs all of the steps listed in
      * <code>BundleContext.installBundle(String location)</code>, except that
      * the bundle's content will be read from the <code>InputStream</code>
      * object. The location identifier string specified will be used as the
      * identity of the bundle.
      *
      * <p>
      * This method must always close the <code>InputStream</code> object, even
      * if an exception is thrown.
      *
      * @param location The location identifier of the bundle to install.
      * @param input The <code>InputStream</code> object from which this bundle
      * will be read.
      * @return The <code>Bundle</code> object of the installed bundle.
      * @throws BundleException If the provided stream cannot be read or the
      * installation failed.
      * @throws java.lang.SecurityException If the caller does not have the
      * appropriate <code>AdminPermission[installed bundle,LIFECYCLE]</code>, and the
      * Java Runtime Environment supports permissions.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      * @see #installBundle(java.lang.String)
      */
     public Bundle installBundle(String location, InputStream input)
             throws BundleException;

     /**
      * Returns the bundle with the specified identifier.
      *
      * @param id The identifier of the bundle to retrieve.
      * @return A <code>Bundle</code> object or <code>null</code> if the
      * identifier does not match any installed bundle.
      */
     public Bundle getBundle(long id);

     /**
      * Returns a list of all installed bundles.
      * <p>
      * This method returns a list of all bundles installed in the OSGi
      * environment at the time of the call to this method. However, since the
      * Framework is a very dynamic environment, bundles can be installed or
      * uninstalled at anytime.
      *
      * @return An array of <code>Bundle</code> objects, one object per
      * installed bundle.
      */
     public Bundle[] getBundles();

     /**
      * Adds the specified <code>ServiceListener</code> object with the
      * specified <code>filter</code> to the context bundle's list of
      * listeners. See {@link Filter} for a description of the filter syntax.
      * <code>ServiceListener</code> objects are notified when a service has a
      * lifecycle state change.
      *
      * <p>
      * If the context bundle's list of listeners already contains a listener
      * <code>l</code> such that <code>(l==listener)</code>, then this
      * method replaces that listener's filter (which may be <code>null</code>)
      * with the specified one (which may be <code>null</code>).
      *
      * <p>
      * The listener is called if the filter criteria is met. To filter based
      * upon the class of the service, the filter should reference the
      * {@link Constants#OBJECTCLASS} property. If <code>filter</code> is
      * <code>null</code>, all services are considered to match the filter.
      *
      * <p>
      * When using a <code>filter</code>, it is possible that the
      * <code>ServiceEvent</code>s for the complete lifecycle of a service
      * will not be delivered to the listener. For example, if the
      * <code>filter</code> only matches when the property <code>x</code> has
      * the value <code>1</code>, the listener will not be called if the
      * service is registered with the property <code>x</code> not set to the
      * value <code>1</code>. Subsequently, when the service is modified
      * setting property <code>x</code> to the value <code>1</code>, the
      * filter will match and the listener will be called with a
      * <code>ServiceEvent</code> of type <code>MODIFIED</code>. Thus, the
      * listener will not be called with a <code>ServiceEvent</code> of type
      * <code>REGISTERED</code>.
      *
      * <p>
      * If the Java Runtime Environment supports permissions, the
      * <code>ServiceListener</code> object will be notified of a service event
      * only if the bundle that is registering it has the
      * <code>ServicePermission</code> to get the service using at least one of
      * the named classes the service was registered under.
      *
      * @param listener The <code>ServiceListener</code> object to be added.
      * @param filter The filter criteria.
      *
      * @throws InvalidSyntaxException If <code>filter</code> contains an
      * invalid filter string that cannot be parsed.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      *
      * @see ServiceEvent
      * @see ServiceListener
      * @see ServicePermission
      */
     public void addServiceListener(ServiceListener listener,
             String filter) throws InvalidSyntaxException;

     /**
      * Adds the specified <code>ServiceListener</code> object to the context
      * bundle's list of listeners.
      *
      * <p>
      * This method is the same as calling
      * <code>BundleContext.addServiceListener(ServiceListener listener,
      * String filter)</code>
      * with <code>filter</code> set to <code>null</code>.
      *
      * @param listener The <code>ServiceListener</code> object to be added.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      *
      * @see #addServiceListener(ServiceListener, String)
      */
     public void addServiceListener(ServiceListener listener);

     /**
      * Removes the specified <code>ServiceListener</code> object from the
      * context bundle's list of listeners.
      *
      * <p>
      * If <code>listener</code> is not contained in this context bundle's list
      * of listeners, this method does nothing.
      *
      * @param listener The <code>ServiceListener</code> to be removed.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      */
     public void removeServiceListener(ServiceListener listener);

     /**
      * Adds the specified <code>BundleListener</code> object to the context
      * bundle's list of listeners if not already present. BundleListener objects
      * are notified when a bundle has a lifecycle state change.
      *
      * <p>
      * If the context bundle's list of listeners already contains a listener
      * <code>l</code> such that <code>(l==listener)</code>, this method
      * does nothing.
      *
      * @param listener The <code>BundleListener</code> to be added.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      * @throws java.lang.SecurityException If listener is a
      * <code>SynchronousBundleListener</code> and the caller does not
      * have the appropriate <code>AdminPermission[context bundle,LISTENER]</code>,
      * and the Java Runtime Environment supports permissions.
      *
      * @see BundleEvent
      * @see BundleListener
      */
     public void addBundleListener(BundleListener listener);

     /**
      * Removes the specified <code>BundleListener</code> object from the
      * context bundle's list of listeners.
      *
      * <p>
      * If <code>listener</code> is not contained in the context bundle's list
      * of listeners, this method does nothing.
      *
      * @param listener The <code>BundleListener</code> object to be removed.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      * @throws java.lang.SecurityException If listener is a
      * <code>SynchronousBundleListener</code> and the caller does not
      * have the appropriate <code>AdminPermission[context bundle,LISTENER]</code>,
      * and the Java Runtime Environment supports permissions.
      */
     public void removeBundleListener(BundleListener listener);

     /**
      * Adds the specified <code>FrameworkListener</code> object to the context
      * bundle's list of listeners if not already present. FrameworkListeners are
      * notified of general Framework events.
      *
      * <p>
      * If the context bundle's list of listeners already contains a listener
      * <code>l</code> such that <code>(l==listener)</code>, this method
      * does nothing.
      *
      * @param listener The <code>FrameworkListener</code> object to be added.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      *
      * @see FrameworkEvent
      * @see FrameworkListener
      */
     public void addFrameworkListener(FrameworkListener listener);

     /**
      * Removes the specified <code>FrameworkListener</code> object from the
      * context bundle's list of listeners.
      *
      * <p>
      * If <code>listener</code> is not contained in the context bundle's list
      * of listeners, this method does nothing.
      *
      * @param listener The <code>FrameworkListener</code> object to be
      * removed.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      */
     public void removeFrameworkListener(FrameworkListener listener);

     /**
      * Registers the specified service object with the specified properties
      * under the specified class names into the Framework. A
      * <code>ServiceRegistration</code> object is returned. The
      * <code>ServiceRegistration</code> object is for the private use of the
      * bundle registering the service and should not be shared with other
      * bundles. The registering bundle is defined to be the context bundle.
      * Other bundles can locate the service by using either the
      * {@link #getServiceReferences} or {@link #getServiceReference} method.
      *
      * <p>
      * A bundle can register a service object that implements the
      * {@link ServiceFactory} interface to have more flexibility in providing
      * service objects to other bundles.
      *
      * <p>
      * The following steps are required to register a service:
      * <ol>
      * <li>If <code>service</code> is not a <code>ServiceFactory</code>,
      * an <code>IllegalArgumentException</code> is thrown if
      * <code>service</code> is not an <code>instanceof</code> all the
      * classes named.
      * <li>The Framework adds these service properties to the specified
      * <code>Dictionary</code> (which may be <code>null</code>): a property
      * named {@link Constants#SERVICE_ID} identifying the registration number of
      * the service and a property named {@link Constants#OBJECTCLASS} containing
      * all the specified classes. If any of these properties have already been
      * specified by the registering bundle, their values will be overwritten by
      * the Framework.
      * <li>The service is added to the Framework service registry and may now
      * be used by other bundles.
      * <li>A service event of type {@link ServiceEvent#REGISTERED} is
      * fired.
      * <li>A <code>ServiceRegistration</code> object for this registration is
      * returned.
      * </ol>
      *
      * @param clazzes The class names under which the service can be located.
      * The class names in this array will be stored in the service's
      * properties under the key {@link Constants#OBJECTCLASS}.
      * @param service The service object or a <code>ServiceFactory</code>
      * object.
      * @param properties The properties for this service. The keys in the
      * properties object must all be <code>String</code> objects. See
      * {@link Constants} for a list of standard service property keys.
      * Changes should not be made to this object after calling this
      * method. To update the service's properties the
      * {@link ServiceRegistration#setProperties} method must be called.
      * The set of properties may be <code>null</code> if the service
      * has no properties.
      *
      * @return A <code>ServiceRegistration</code> object for use by the bundle
      * registering the service to update the service's properties or to
      * unregister the service.
      *
      * @throws java.lang.IllegalArgumentException If one of the following is
      * true:
      * <ul>
      * <li><code>service</code> is <code>null</code>.
      * <li><code>service</code> is not a <code>ServiceFactory</code>
      * object and is not an instance of all the named classes in
      * <code>clazzes</code>.
      * <li><code>properties</code> contains case variants of the same
      * key name.
      * </ul>
      *
      * @throws java.lang.SecurityException If the caller does not have the
      * <code>ServicePermission</code> to register the service for all
      * the named classes and the Java Runtime Environment supports
      * permissions.
      *
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      *
      * @see ServiceRegistration
      * @see ServiceFactory
      */
     public ServiceRegistration registerService(String [] clazzes,
             Object service, Dictionary properties);

     /**
      * Registers the specified service object with the specified properties
      * under the specified class name with the Framework.
      *
      * <p>
      * This method is otherwise identical to
      * {@link #registerService(java.lang.String[], java.lang.Object,
      * java.util.Dictionary)} and is provided as a convenience when
      * <code>service</code> will only be registered under a single class name.
      * Note that even in this case the value of the service's
      * {@link Constants#OBJECTCLASS} property will be an array of strings,
      * rather than just a single string.
      *
      * @param clazz The class name under which the service can be located.
      * @param service The service object or a <code>ServiceFactory</code>
      * object.
      * @param properties The properties for this service.
      *
      * @return A <code>ServiceRegistration</code> object for use by the bundle
      * registering the service to update the service's properties or to
      * unregister the service.
      *
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      * @see #registerService(java.lang.String[], java.lang.Object,
      * java.util.Dictionary)
      */
     public ServiceRegistration registerService(String clazz,
             Object service, Dictionary properties);

     /**
      * Returns an array of <code>ServiceReference</code> objects. The returned
      * array of <code>ServiceReference</code> objects contains services that
      * were registered under the specified class, match the specified filter
      * criteria, and the packages for the class names under which the services
      * were registered match the context bundle's packages as defined in
      * {@link ServiceReference#isAssignableTo(Bundle, String)}.
      *
      * <p>
      * The list is valid at the time of the call to this method, however since
      * the Framework is a very dynamic environment, services can be modified or
      * unregistered at anytime.
      *
      * <p>
      * <code>filter</code> is used to select the registered service whose
      * properties objects contain keys and values which satisfy the filter. See
      * {@link Filter} for a description of the filter string syntax.
      *
      * <p>
      * If <code>filter</code> is <code>null</code>, all registered services
      * are considered to match the filter. If <code>filter</code> cannot be
      * parsed, an {@link InvalidSyntaxException} will be thrown with a human
      * readable message where the filter became unparsable.
      *
      * <p>
      * The following steps are required to select a set of
      * <code>ServiceReference</code> objects:
      * <ol>
      * <li>If the filter string is not <code>null</code>, the filter string
      * is parsed and the set <code>ServiceReference</code> objects of
      * registered services that satisfy the filter is produced. If the filter
      * string is <code>null</code>, then all registered services are
      * considered to satisfy the filter.
      * <li>If the Java Runtime Environment supports permissions, the set of
      * <code>ServiceReference</code> objects produced by the previous step is
      * reduced by checking that the caller has the
      * <code>ServicePermission</code> to get at least one of the class names
      * under which the service was registered. If the caller does not have the
      * correct permission for a particular <code>ServiceReference</code>
      * object, then it is removed from the set.
      * <li>If <code>clazz</code> is not <code>null</code>, the set is
      * further reduced to those services that are an <code>instanceof</code>
      * and were registered under the specified class. The complete list of
      * classes of which a service is an instance and which were specified when
      * the service was registered is available from the service's
      * {@link Constants#OBJECTCLASS} property.
      * <li>The set is reduced one final time by cycling through each
      * <code>ServiceReference</code> object and calling
      * {@link ServiceReference#isAssignableTo(Bundle, String)} with the context
      * bundle and each class name under which the <code>ServiceReference</code>
      * object was registered. For any given <code>ServiceReference</code>
      * object, if any call to
      * {@link ServiceReference#isAssignableTo(Bundle, String)} returns
      * <code>false</code>, then it is removed from the set of
      * <code>ServiceReference</code> objects.
      * <li>An array of the remaining <code>ServiceReference</code> objects is
      * returned.
      * </ol>
      *
      * @param clazz The class name with which the service was registered or
      * <code>null</code> for all services.
      * @param filter The filter criteria.
      * @return An array of <code>ServiceReference</code> objects or
      * <code>null</code> if no services are registered which satisfy
      * the search.
      * @throws InvalidSyntaxException If <code>filter</code> contains an
      * invalid filter string that cannot be parsed.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      */
     public ServiceReference[] getServiceReferences(String clazz,
             String filter) throws InvalidSyntaxException;

     /**
      * Returns an array of <code>ServiceReference</code> objects. The returned
      * array of <code>ServiceReference</code> objects contains services that
      * were registered under the specified class and match the specified filter
      * criteria.
      *
      * <p>
      * The list is valid at the time of the call to this method, however since
      * the Framework is a very dynamic environment, services can be modified or
      * unregistered at anytime.
      *
      * <p>
      * <code>filter</code> is used to select the registered service whose
      * properties objects contain keys and values which satisfy the filter. See
      * {@link Filter} for a description of the filter string syntax.
      *
      * <p>
      * If <code>filter</code> is <code>null</code>, all registered services
      * are considered to match the filter. If <code>filter</code> cannot be
      * parsed, an {@link InvalidSyntaxException} will be thrown with a human
      * readable message where the filter became unparsable.
      *
      * <p>
      * The following steps are required to select a set of
      * <code>ServiceReference</code> objects:
      * <ol>
      * <li>If the filter string is not <code>null</code>, the filter string
      * is parsed and the set <code>ServiceReference</code> objects of
      * registered services that satisfy the filter is produced. If the filter
      * string is <code>null</code>, then all registered services are
      * considered to satisfy the filter.
      * <li>If the Java Runtime Environment supports permissions, the set of
      * <code>ServiceReference</code> objects produced by the previous step is
      * reduced by checking that the caller has the
      * <code>ServicePermission</code> to get at least one of the class names
      * under which the service was registered. If the caller does not have the
      * correct permission for a particular <code>ServiceReference</code>
      * object, then it is removed from the set.
      * <li>If <code>clazz</code> is not <code>null</code>, the set is
      * further reduced to those services that are an <code>instanceof</code>
      * and were registered under the specified class. The complete list of
      * classes of which a service is an instance and which were specified when
      * the service was registered is available from the service's
      * {@link Constants#OBJECTCLASS} property.
      * <li>An array of the remaining <code>ServiceReference</code> objects is
      * returned.
      * </ol>
      *
      * @param clazz The class name with which the service was registered or
      * <code>null</code> for all services.
      * @param filter The filter criteria.
      * @return An array of <code>ServiceReference</code> objects or
      * <code>null</code> if no services are registered which satisfy
      * the search.
      * @throws InvalidSyntaxException If <code>filter</code> contains an
      * invalid filter string that cannot be parsed.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      * @since 1.3
      */
     public ServiceReference[] getAllServiceReferences(String clazz,
             String filter) throws InvalidSyntaxException;

     /**
      * Returns a <code>ServiceReference</code> object for a service that
      * implements and was registered under the specified class.
      *
      * <p>
      * This <code>ServiceReference</code> object is valid at the time of the
      * call to this method, however as the Framework is a very dynamic
      * environment, services can be modified or unregistered at anytime.
      *
      * <p>
      * This method is the same as calling
      * {@link BundleContext#getServiceReferences(String, String)} with a
      * <code>null</code> filter string. It is provided as a convenience for
      * when the caller is interested in any service that implements the
      * specified class.
      * <p>
      * If multiple such services exist, the service with the highest ranking (as
      * specified in its {@link Constants#SERVICE_RANKING} property) is returned.
      * <p>
      * If there is a tie in ranking, the service with the lowest service ID (as
      * specified in its {@link Constants#SERVICE_ID} property); that is, the
      * service that was registered first is returned.
      *
      * @param clazz The class name with which the service was registered.
      * @return A <code>ServiceReference</code> object, or <code>null</code>
      * if no services are registered which implement the named class.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      * @see #getServiceReferences(String, String)
      */
     public ServiceReference getServiceReference(String clazz);

     /**
      * Returns the specified service object for a service.
      * <p>
      * A bundle's use of a service is tracked by the bundle's use count of that
      * service. Each time a service's service object is returned by
      * {@link #getService(ServiceReference)} the context bundle's use count for
      * that service is incremented by one. Each time the service is released by
      * {@link #ungetService(ServiceReference)} the context bundle's use count
      * for that service is decremented by one.
      * <p>
      * When a bundle's use count for a service drops to zero, the bundle should
      * no longer use that service.
      *
      * <p>
      * This method will always return <code>null</code> when the service
      * associated with this <code>reference</code> has been unregistered.
      *
      * <p>
      * The following steps are required to get the service object:
      * <ol>
      * <li>If the service has been unregistered, <code>null</code> is
      * returned.
      * <li>The context bundle's use count for this service is incremented by
      * one.
      * <li>If the context bundle's use count for the service is currently one
      * and the service was registered with an object implementing the
      * <code>ServiceFactory</code> interface, the
      * {@link ServiceFactory#getService(Bundle, ServiceRegistration)} method is
      * called to create a service object for the context bundle. This service
      * object is cached by the Framework. While the context bundle's use count
      * for the service is greater than zero, subsequent calls to get the
      * services's service object for the context bundle will return the cached
      * service object. <br>
      * If the service object returned by the <code>ServiceFactory</code>
      * object is not an <code>instanceof</code> all the classes named when the
      * service was registered or the <code>ServiceFactory</code> object throws
      * an exception, <code>null</code> is returned and a Framework event of
      * type {@link FrameworkEvent#ERROR} is fired.
      * <li>The service object for the service is returned.
      * </ol>
      *
      * @param reference A reference to the service.
      * @return A service object for the service associated with
      * <code>reference</code> or <code>null</code> if the service is
      * not registered or does not implement the classes under which it
      * was registered in the case of a <code>ServiceFactory</code>.
      * @throws java.lang.SecurityException If the caller does not have the
      * <code>ServicePermission</code> to get the service using at
      * least one of the named classes the service was registered under
      * and the Java Runtime Environment supports permissions.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      * @see #ungetService(ServiceReference)
      * @see ServiceFactory
      */
     public Object getService(ServiceReference reference);

     /**
      * Releases the service object referenced by the specified
      * <code>ServiceReference</code> object. If the context bundle's use count
      * for the service is zero, this method returns <code>false</code>.
      * Otherwise, the context bundle's use count for the service is decremented
      * by one.
      *
      * <p>
      * The service's service object should no longer be used and all references
      * to it should be destroyed when a bundle's use count for the service drops
      * to zero.
      *
      * <p>
      * The following steps are required to unget the service object:
      * <ol>
      * <li>If the context bundle's use count for the service is zero or the
      * service has been unregistered, <code>false</code> is returned.
      * <li>The context bundle's use count for this service is decremented by
      * one.
      * <li>If the context bundle's use count for the service is currently zero
      * and the service was registered with a <code>ServiceFactory</code>
      * object, the
      * {@link ServiceFactory#ungetService(Bundle, ServiceRegistration, Object)}
      * method is called to release the service object for the context bundle.
      * <li><code>true</code> is returned.
      * </ol>
      *
      * @param reference A reference to the service to be released.
      * @return <code>false</code> if the context bundle's use count for the
      * service is zero or if the service has been unregistered;
      * <code>true</code> otherwise.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      * @see #getService
      * @see ServiceFactory
      */
     public boolean ungetService(ServiceReference reference);

     /**
      * Creates a <code>File</code> object for a file in the persistent storage
      * area provided for the bundle by the Framework. This method will return
      * <code>null</code> if the platform does not have file system support.
      *
      * <p>
      * A <code>File</code> object for the base directory of the persistent
      * storage area provided for the context bundle by the Framework can be
      * obtained by calling this method with an empty string as
      * <code>filename</code>.
      *
      * <p>
      * If the Java Runtime Environment supports permissions, the Framework will
      * ensure that the bundle has the <code>java.io.FilePermission</code> with
      * actions <code>read</code>,<code>write</code>,<code>delete</code>
      * for all files (recursively) in the persistent storage area provided for
      * the context bundle.
      *
      * @param filename A relative name to the file to be accessed.
      * @return A <code>File</code> object that represents the requested file
      * or <code>null</code> if the platform does not have file system
      * support.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      */
     public File getDataFile(String filename);

     /**
      * Creates a <code>Filter</code> object. This <code>Filter</code> object
      * may be used to match a <code>ServiceReference</code> object or a
      * <code>Dictionary</code> object.
      *
      * <p>
      * If the filter cannot be parsed, an {@link InvalidSyntaxException} will be
      * thrown with a human readable message where the filter became unparsable.
      *
      * @param filter The filter string.
      * @return A <code>Filter</code> object encapsulating the filter string.
      * @throws InvalidSyntaxException If <code>filter</code> contains an
      * invalid filter string that cannot be parsed.
      * @throws NullPointerException If <code>filter</code> is null.
      * @throws java.lang.IllegalStateException If this BundleContext is no
      * longer valid.
      *
      * @since 1.1
      * @see "Framework specification for a description of the filter string syntax."
      * @see FrameworkUtil#createFilter(String)
      */
     public Filter createFilter(String filter)
             throws InvalidSyntaxException;
 }

